Catalysts for hydrosilylation reactions

ABSTRACT

The invention relates to metal complexes of formula (I)                    
     These complexes are particularly suitable for use as catalysts of hydrosilylation reactions.

The invention relates to a catalyst which is appropriate for catalyzinghydrosilylation reactions.

The addition of an organosilylated compound having an Si—H unit to anolefin or to an acetylene derivative through the formation of acarbon-silicon bond (hydrosilylation reaction) is conventionally carriedout in the presence of a metal catalyst. The hydrosilylation reaction isschematically represented in the following manner in the case ofolefins:

As an example of a catalyst, platinum catalysts have been recommended bynumerous authors. Thus, U.S. Pat. No. 2,823,218 describes achloroplatinic acid as catalyst. U.S. Pat. No. 2,970,150 proposes theuse of metallic platinum on a finely divided support. Thehydrosilylation methods described in these patents are however, not veryattractive from an economic point of view since they require the use oflarge quantities of platinum catalyst.

Thus, up until now, most industrial hydrosilylation reactions arecatalyzed by the Karstedt solution which consists of complexes ofplatinum having the oxidation number 0. The general formula of theKarstedt complex is Pt₂(tetramethyldivinylsiloxane)₃:

where Me represents methyl.

One of the disadvantages of this catalyst lies in the possibleinstability of the catalyst during the course of a reaction: it has beenpossible to observe the precipitation of metallic platinum and theformation of insoluble colloids in the reaction medium: this instabilityof the catalyst in the reaction medium has the effect of reducing thecatalytic activity. Furthermore, it results in cloudy and highly coloredsolutions which are not much liked by the user since they lead to theformation of highly colored hydrosilylation products.

Another major disadvantage of the Karstedt catalyst is the concomitantformation of by-products of the hydrosilylation reaction: alongside thehydrosilylation products, the products resulting from olefin double bondisomerization reactions and/or hydrogenation reactions are isolated.

One of the objectives of the present invention is therefore to provide astable catalyst complex which makes it possible to limit the sidereactions.

Because of its excellent stability, the complex of the inventionmoreover makes it possible to operate at higher reaction temperatures.

The other advantages of the invention will appear to a person skilled inthe art on reading the preferred embodiments of the invention.

The invention relates more particularly to a metal complex of formula I:

in which:

M represents a metal having an oxidation number 0 chosen from the group8 metals in the Periodic Table as published in the Handbook of Chemistryand Physics, 65^(th) edition, 1984-1985;

X represents O, NR_(a) or CR_(f)R_(g);

Y₁ and Y₂ represent, independently of each other, CR_(b)R_(c) orSiR_(d)R_(e);

R₁, R₂, R₅ and R₆, which are identical or different, are chosen from ahydrogen atom, an alkyl group and an aryl group optionally substitutedwith alkyl;

R₃, R₄, R_(a), R_(b), R_(c), are independently chosen from a hydrogenatom; an alkyl group; an acyl group; an aryl group optionallysubstituted with alkyl; a cycloalkyl group optionally substituted withalkyl; and an arylalkyl group in which the aryl portion is optionallysubstituted with alkyl;

R_(d) and R_(e) are independently chosen from alkenyl; alkynyl; alkyl;alkoxy; acyl; aryl optionally substituted with alkyl; cycloalkyloptionally substituted with alkyl; and arylalkyl in which the arylportion is optionally substituted with alkyl; or alternatively

when Y₁ and Y₂ independently represent SiR_(d)R_(e), two R_(d) groupslinked to two separate silicon atoms together form a chain of formula:

in which n is an integer from 1 to 3; X is as defined above; R and R′,which are identical or different, take any one of the meanings givenabove for R_(e), it being understood that when n is 2 or 3, a singlesilicon atom of said chain may be substituted with one or two alkenyl oralkynyl groups;

or alternatively when Y₁ and Y₂ independently represent SiR_(d)R_(e),two R_(d) groups linked to separate silicon atoms together form asaturated hydrocarbon chain, the two R_(b) groups together with saidsilicon atoms and X forming a 6- to 10-membered ring; or alternatively

when Y₁ and Y₂ independently represent CR_(b)R_(c), two R_(b) groupslinked to separate carbon atoms together form a saturated hydrocarbonchain, the two R_(b) groups together with the carbon atoms carrying themand X form a 6- to 10-membered ring;

R_(f) and R_(g) represent, independently of each other, a hydrogen atom;an alkyl group; an acyl group; an aryl group optionally substituted withalkyl; a cycloalkyl group optionally substituted with alkyl; anarylalkyl group in which the aryl portion is optionally substituted withalkyl; a halogen atom; an alkenyl group; an alkynyl group; or a groupSiG₁G₂G₃ where G₁, G₂ and G₃ are, independently of each other, alkyl;alkoxy; aryl optionally substituted with alkyl or alkoxy; or arylalkylin which the aryl portion is optionally substituted with alkyl oralkoxy;

L represents a carbene of formula II.1 or II.2:

in which:

A and B independently represent C or N, it being understood that when Arepresents N, then T₄ represents nothing and when B represents N, thenT₃ represents nothing;

T₃ and T₄ independently represent a hydrogen atom; an alkyl group; acycloalkyl group optionally substituted with alkyl or alkoxy; an arylgroup optionally substituted with alkyl or alkoxy; an alkenyl group; analkynyl group; or an arylalkyl group in which the aryl portion isoptionally substituted with alkyl or alkoxy;

T₁ and T₂ independently represent an alkyl group; an alkyl group whichis perfluorinated or optionally substituted with a perfluoroalkyl group;a cycloalkyl group optionally substituted with alkyl or alkoxy; an arylgroup optionally substituted with alkyl or alkoxy; an alkenyl group; analkynyl group; or an arylalkyl group in which the aryl portion isoptionally substituted with alkyl or alkoxy; or alternatively

the substituents T₁, T₂, T₃ and T₄, may form in pairs, when they arelocated on two adjacent summits in the formulae II.1 and II.2, asaturated or unsaturated hydrocarbon chain.

According to the invention, the oxidation number 0 of the metal M is anessential characteristic of the invention.

Preferably, the group 8 metals which M represents are palladium,platinum or nickel. According to a more preferred embodiment of theinvention, M represents platinum having the oxidation number 0.

The expression alkyl is understood to mean, according to the invention,a linear or branched, saturated hydrocarbon chain, preferably havingfrom 1 to 10 carbon atoms, for example from 1 to 8 carbon atoms, evenbetter from 1 to 7 carbon atoms.

Examples of alkyl groups are in particular methyl, ethyl, isopropyl,n-propyl, tert-butyl, isobutyl, n-butyl, n-pentyl, isoamyl and1,1-dimethylpropyl.

According to the invention, the alkyl portion of the alkoxy radical isas defined above.

The alkyl radical which is perfluorinated or optionally substituted witha perfluoroalkyl group preferably has the formula:

—(CH₂)_(p)—C_(q)F_(2q+1)

in which p represents 0, 1, 2, 3 or 4; q is an integer from 1 to 10; andC_(q)F_(2q+1) is linear or branched. Preferred examples of this radicalare: —(CH₂)₂—(CF₂)₅—CF₃ and —(CF₂)₇—CF₃.

The expression aryl denotes an aromatic hydrocarbon group having from 6to 18 carbon atoms, which is monocyclic or polycyclic, and preferablymonocyclic or bicyclic. It should be understood that in the context ofthe invention, the expression polycyclic aromatic radical is understoodto mean a radical having two or more aromatic rings, condensed to eachother, that is to say having, in pairs, at least two carbons in common.By way of example, there may be mentioned the phenyl, naphthyl, anthryland phenanthryl radicals.

The expression arylalkyl denotes an alkyl group as defined above,substituted with one or more aryl groups on its hydrocarbon chain, thearyl group being as defined above. Examples thereof are benzyl andtriphenylmethyl.

The expression acyl is understood to mean, according to the invention, agroup R_(o)—CO— where R_(o) represents alkyl as defined above; oralternatively a group Ar—CO— where Ar represents an aryl group asdefined above, or alternatively an arylalkyl in which aryl and alkyl areas defined above and in which the aryl portion is optionally substitutedwith alkyl.

The expression cycloalkyl is understood to mean a mono- or polycyclic,preferably mono- or bicyclic, saturated hydrocarbon radical preferablyhaving from 3 to 10 carbon atoms, even better from 3 to 8. Theexpression polycyclic saturated hydrocarbon radical is understood tomean a radical having two or more cyclic rings attached to each other byσ bonds and/or condensed in pairs.

Examples of polycyclic cycloalkyl groups are adamantane and norbornane.

Examples of monocyclic cycloalkyl groups are cyclopropyl, cyclobutyl,cyclopentyl, cyclohexyl, cycloheptyl and cyclooctyl.

The expression alkenyl is understood to mean a linear or branchedunsaturated hydrocarbon chain having at least one olefin double bond,and more preferably a single double bond. Preferably, the alkenyl grouphas from 2 to 8 carbon atoms, even better from 2 to 6.

Preferred examples of alkenyl groups are vinyl and allyl groups.

The expression alkynyl is understood to mean, according to theinvention, a linear or branched, unsaturated hydrocarbon chain having atleast one acetylene triple bond, and more preferably a single triplebond. Preferably, the alkynyl group has from 2 to 8 carbon atoms, evenbetter from 2 to 6 carbon atoms. By way of example, there may bementioned the acetylenyl group, as well as the propargyl group.

According to a preferred embodiment of the invention, Y₁ and Y₂ eitherboth represent CR_(b)R_(c), or both SiR_(d)R_(e), such that thepreferred compounds of the invention either have the formula I.1, or theformula I.2:

where

R_(b) ¹ and R_(c) ¹ are the substituents R_(b) and R_(c) of Y₁ informula I.1;

R_(b) ² and R_(c) ² are the substituents R_(b) and R_(c) of Y₂ informula I.2;

R_(d) ¹ and R_(e) ¹ are the substituents R_(d) and R_(e) of Y₁ informula I.1;

R_(d) ² and R_(e) ² are the substituents R_(d) and R_(e) of Y₂ informula I.2.

Thus, R_(b) ¹ may be identical to or different from R_(b) ²; R_(c) ¹ maybe identical to or different from R_(c) ²; R_(d) ¹ may be identical toor different from R_(d) ²; and R_(e) ¹ may be identical to or differentfrom R_(e) ².

Preferably, R_(b) ¹=R_(b) ²; R_(c) ¹=R_(c) ²; R_(d) ¹=R_(d) ²; and R_(e)¹=R_(e) ².

Among the latter compounds those for which R₃=R₄; R₅=R₂; and R₁=R₆ arefurther preferred.

According to another preferred variant of the invention, R_(d) ¹ andR_(d) ² together form:

(a) either a chain

 in which n is an integer from 1 to 3; X is as defined above; and R andR′, which are identical or different, take any one of the meanings givenabove for R_(e), it being understood that when n is 2 or 3, a singlesilicon atom of said chain may be substituted with one or two alkenyl oralkynyl groups;

(b) or a saturated hydrocarbon chain such that the two substituentsR_(d), together with the two silicon atoms carrying them and X, form a6- to 10-membered, preferably 6- to 8-membered, ring.

When R_(d) ¹ and R_(d) ² form the chain (a), it is preferable for n tobe equal to 1 or 2 (even better n is equal to 1) and that R=R_(e), thetwo groups R_(e) carried by the two silicon atoms being identical. Inthis case, R_(e) preferably represents alkyl, for example methyl. Evenbetter, in these compounds, R′ represents —CR₃═CR₁R₂ and R₁=R₆; R₅=R₂;and R₃=R₄.

When R_(d) ¹ and R_(d) ² form the chain (b), it is preferable for thetwo groups R_(d), together with the two silicon atoms and the group X,to form an 8-membered ring. In this case, it is preferable that R_(e) ¹is identical to R_(e) ². These compounds have the general formula:

where T represents alkyl, i is an integer between 0 and 5, T beinglocated on one or more of the summits 1, 2, 3, 4 and 5 of the aboveformula.

In the same manner, when Y₁ and Y₂ represent CR_(b)R_(c), the two groupsR_(b) linked to separate carbon atoms may together form a saturatedhydrocarbon chain (c) such that the two groups R_(b) together with thecarbons carrying them and X form a 6- to 10-membered ring. Preferably,the ring formed is an 8-membered ring, in which case the metal complexcorresponds to the formula:

where T represents alkyl; i is an integer between 0 and 5, T beinglocated on one or more of the summits 1, 2, 3, 4 and 5 of the formulaabove.

In the context of the invention, two groups R_(d) linked to two separatesilicon atoms may form a chain of formula:

When this is the case, it is preferable that X represents O in thecompounds of the invention. These preferred compounds have the generalformula:

Among these compounds, it is preferable that R_(e) ¹=R_(e) ².Advantageously R_(e) ¹=R_(e) ² represents alkyl (for example methyl).

Preferably, n is equal to 1 or 2 and R=R_(e) ¹, it being understood thatwhen n is equal to 2, a single silicon atom of the chain O—(SiRR′—O)_(n)may be substituted with one or two alkenyl or alkynyl groups. Evenbetter, R′=—CR₃═CR₁R₂ and R₁=R₆; R₂=R₅ and R₃=R₄.

The expression “represents nothing” means that the substituents —T₃,respectively —T₄, are nonexistent. Indeed, in the formulae II.1 andII.2, the nitrogen atom is trivalent, such that when A or B representsN, the nitrogen atom cannot have an additional substituent.

According to a particular embodiment of the invention, the carbenes offormulae II.1 and II.2 have at least two condensed rings, that is to saythat at least two substituents among T₁, T₂, T₃ and T₄, situated on twoadjacent summits, together form a saturated or unsaturated hydrocarbonchain preferably having from 3 to 6 carbon atoms. The expressionsaturated or unsaturated hydrocarbon chain is understood to mean alinear or branched hydrocarbon chain which may or may not have one ormore unsaturations of the olefin double bond or acetylene triple bondtype.

When the carbenes II.1 and II.2 have two condensed rings, they thereforecorrespond to one of the following formulae, in which (alk) represents asaturated or unsaturated hydrocarbon chain:

It should be understood however that the carbenes II.1 and II.2 may havemore than two condensed rings.

When R_(f) and/or R_(g) represents SiG₁G₂G₃, it is preferable that R_(f)and/or R_(g) are trialkylsilyl, for example SiG₁G₂G₃ whereG₁=G₂=G₃=alkyl.

Subgroups of the metal complexes of the invention consist of thecomplexes for which:

X=O; Y₁ and Y₂ independently represent SiR_(d)R_(e); or

X=NR_(a); Y₁ and Y₂ independently represent CR_(b)R_(c); or

X=NR_(a); Y₁ and Y₂ independently represent SiR_(d)R_(e); or

X=CR_(f)R_(g); Y₁ and Y₂ independently represent CR_(b)R_(c); or

X=CR_(f)R_(g); Y₁ and Y₂ independently represent SiR_(d)R_(e).

Among these metal complexes of formula I, there are preferred those forwhich:

when X represents O, Y₁ and Y₂ independently represent SiR_(d)R_(e); or

when X represents NR_(a), Y₁ and Y₂ independently represent CR_(b)R_(c);or

when X represents CR_(f)R_(g), Y₁ and Y₂ independently representCR_(b)R_(c).

Most preferably, X represents O and Y₁ and Y₂ independently representSiR_(d)R_(e) in the metal complex of formula I. In the context of theinvention, the expression “independently represent” means that thesubstituents designated are either identical or different.

Still preferably, R₁, R₂, R₅ and R₆ are hydrogen atoms.

Preferred meanings of R₃ and R₄ are in particular a hydrogen atom; analkyl group; an aryl group optionally substituted with alkyl; and acycloalkyl group optionally substituted with alkyl. Among thesepreferred meanings, it is particularly advantageous that R₃ and R₄,which are identical, represent a hydrogen atom; (C₃-C₈)cycloalkyl or(C₁-C₈)alkyl.

Still preferably, the diolefin ligand of the complex of formula I issymmetric, that is to say that R₅=R₂; R₆=R₁; R₃=R₄ and the two groupsY₁, Y₂ are strictly identical to each other, that is Y₁=CR_(b) ¹R_(c)and Y₂=CR_(b) ²R_(c) where R_(b) ¹ and R_(b) ² together form a symmetricchain, or alternatively Y₁=SiR_(d) ¹R_(e) and Y₂=SiR_(d) ²R_(e) whereR_(d) ¹ and R_(d) ² together form a symmetric chain.

A preferred group of complexes according to the invention consists ofthe complexes of formula I in which L represents a carbene of formulaII.1.

Preferably, A and B in the formulae II.1 and II.2 both represent acarbon atom.

Preferred meanings of T₁ and T₂ are alkyl; cycloalkyl; arylalkyl; andaryl which is optionally substituted with alkyl.

Preferred meanings of T₃ and T₄ are hydrogen; alkyl; cycloalkyl;arylalkyl; and aryl which is optionally substituted with alkyl.

Preferably, when T₁, T₂, T₃ or T₄ represents alkyl, then alkyl ismethyl, isopropyl or tert-butyl.

Likewise, when T₁, T₂, T₃ or T₄ represents aryl, then aryl is phenyl.

When T₁, T₂, T₃ or T₄ represents aryl optionally substituted with alkyl,then T₁, T₂, T₃ or T₄ is tolyl or xylyl.

When T₁, T₂, T₃ or T₄ represents arylalkyl, then arylalkyl is preferablybenzyl or triphenylmethyl.

When T₁, T₂, T₃ or T₄ represents cycloalkyl, then cycloalkyl ispreferably cyclopentyl, cyclohexyl or adamantyl.

A preferred group of complexes of formula I consists of the complexesfor which in the carbene of formulae II.1 or II.2, T₃ and T₄ represent ahydrogen atom.

Likewise, the complexes of formula I in which T₁ and T₂ are chosen from(C₁-C₈)alkyl and (C₃-C₈)-cycloalkyl form a preferred subgroup. Evenbetter, T₁ and T₂ are identical and represent (C₃-C₈)cycloalkyl.

Advantageously, T₁ and T₂, which are identical or different, represent(C₁-C₈)alkyl or (C₃-C₈)-cycloalkyl; or alternatively R₃ and R₄, whichare identical or different, represent (C₁-C₈)alkyl or (C₃-C₈)cycloalkyl;or still alternatively T₁, T₂, R₃ and R₄, which are identical ordifferent, represent (C₁-C₈)alkyl or (C₃-C₈)cycloalkyl.

A particularly preferred group of metal complexes of formula I consistsof the complexes of formula:

in which:

R₃ represents a hydrogen atom; a (C₁-C₈)alkyl group; or a(C₃-C₈)cycloalkyl group optionally substituted with (C₁-C₄)alkyl;

T₁ and T₂ are identical and represent (C₁-C₈)alkyl or (C₃-C₈)cycloalkyl;

R_(d) and R_(e) are as defined above.

Other preferred subgroups of the invention are defined as follows:

Metal complexes of formula I in which Y₁ and Y₂, which are identical,represent SiR_(d)R_(e); R₁=R₂=R₃=R₄=R₅=R₆=H; X=O; R_(d) and R_(e) areindependently chosen from alkyl; aryl optionally substituted with alkyl;alkenyl; and alkynyl.

Metal complexes of formula I in which Y₁ and Y₂, which are identical,represent SiR_(d)R_(e); X=O; R₁=R₆; R₂=R₅; R₃=R₄; R₁ and R₂independently represent alkyl; R₃ represents alkyl or aryl optionallysubstituted with alkyl; R_(d) and R_(e) independently represent alkyl;alkenyl; alkynyl; or aryl optionally substituted with alkyl.

Metal complexes of formula I in which Y₁ and Y₂, which are identical,represent SiR_(d)R_(e); X=O; R₁=R₂=R₃=R₄=R₅=R₆=H; and R_(d)=R_(e)=methylor alternatively R_(d)=methyl and R_(e)=phenyl.

Metal complexes of formula I in which Y₁ and Y₂, which are identical,represent SiR_(d)R_(e); X=O; R₁=R₃=R₄=R₆=H; R₂=R₅=alkyl.

Metal complexes of formula I in which Y₁ and Y₂, which are identical,represent SiR_(d)R_(e); X=CR_(f)R_(g); R_(f)=R_(g)=a hydrogen atom;R_(d) and R_(e), which are identical or different, are chosen fromalkyl; and aryl optionally substituted with alkyl; R₁=R₆; R₂=R₅; R₃=R₄;R₁ and R₂ are chosen from a hydrogen atom and an alkyl group; R₃represents a hydrogen atom, alkyl or aryl optionally substituted withalkyl.

Metal complexes of formula I in which Y₁ and Y₂, which are identical,represent SiR_(d)R_(e); X=CR_(f)R_(g) where R_(f) and R_(g) represent ahalogen atom, preferably a chlorine atom or a bromine atom;R_(d)=R_(e)=alkyl, preferably methyl; R₁=R₂=R₃=R₄=R₅=R₆=H.

Metal complexes of formula I in which Y₁ and Y₂, which are identical,represent SiR_(d)R_(e); X=CR_(f)R_(g) where R_(f) and R_(g) representSiG₁G₂G₃ such as trialkylsilyl (for example Si(CH₃)₃);R_(d)=R_(e)=alkyl, preferably methyl; R₁=R₂=R₃=R₄=R₅=R₆=H.

Metal complexes of formula I in which X represents —NR_(a); Y₁ and Y₂,which are identical, represent SiR_(d)R_(e); R₁=R₆; R₂=R₅; R₃=R₄.

Metal complexes of formula I in which X represents —NR_(a);Y₁=Y₂=SiR_(d)R_(e); the two groups R_(d) together form the chain

—NR_(a)—(SiR_(e)R_(d) ⁰—NR_(a))_(n)—

in which R_(d) ⁰ represents —CR₃═CR₁R₂; n represents from 1 to 3; R₁=R₆;R₂=R₅; and R₃=R₄.

The complexes of the invention are prepared in a conventional manner,for example from complexes known from the state of the art, by ligandexchange, that is to say addition of the appropriate carbene of formulaII.1 or II.2 to a metal complex of the metal M in solution, designatedprecursor complex.

Appropriate precursor complexes are the Karstedt complex of formula:

Pt₂[ViMe₂Si—O—SiMe₂Vi]₃

in which Vi represents the vinyl radical; and more generally

M₂[R₅R₆C═CR₄—Y₁—X—Y₂—CR₃═CR₁R₂]₃

where M, R₅, R₆, R₄, R₃, R₁, R₂, Y₁, X and Y₂ are as defined above, suchas for example

M₂[CR₅R₆═CR₄—SiR_(d)R_(e)—O—SiR_(d)R_(e)—CR₃═CR₁R₂]₃, it

being understood that M, R₁, R₂, R₃, R₄, R₅, R₆, R_(d) and R_(e) are asdefined above;

Pt(COD)₂ in which COD represents cyclooctadiene and more generallyM(COD)₂ where M is a group 8 metal; or alternatively

metal complexes of olefin and of bisphosphine.

The complexes of formula I are generally prepared from precursorcomplexes having, as ligand, at least one diolefin compound of formulaIII:

in which R₁, R₂, R₃, R₄, R₅, R₆, X, Y₁ and Y₂ are as defined above forformula I.

These ligands are either commercially available, or are easily preparedby a person skilled in the art from commercial compounds.

When X represents NR_(a) and Y₁ and Y₂, independently of each other,represent CR_(b)R_(c), the compounds of formula III are amines which canbe easily prepared using conventional organic chemistry methods. Thus,when R_(a) is different from a hydrogen atom, these amines may be easilyprepared from the corresponding primary amine of formula R_(a)NH₂ by theaction of appropriate chlorides, preferably in the presence of anorganic or inorganic base.

When the diolefin III is symmetric (that is to say that R₄=R₃; R₅=R₂;R₁=R₆; and Y₁=Y₂) , R_(a)NH₂ is reacted with two equivalents of achloride of formula:

Cl—CR_(b)R_(c)—CR₃═CR₁R₂  (IV)

in the presence of a base.

When the diolefin III is disymmetric, it is preferable to protect theamino group of R_(a)NH₂ with an appropriate conventional protectinggroup P before reacting the resulting compound of formula R_(a)NHP withthe chloride of formula V:

Cl—CR_(b) ²R_(c) ²—CR₃═CR₁R₂  (V)

in the presence of an appropriate base.

Then, after deprotection, the resulting amine is reacted with a chlorideof formula:

Cl—CR_(b) ¹R_(c) ¹—CR₄═CR₅R₆  (VI)

in order to obtain the expected amine.

In the formulae IV, V and VI above, the substituents R₁, R₂, R₃, R₄, R₅and R₆ are as defined for formula I; R_(b) ¹ and R_(b) ² are as definedfor R_(b); and R_(c) ¹ and R_(c) ² are as defined for R_(c).

The groups P for protecting the amine functional groups as well as thecorresponding methods of deprotection are described in Protective Groupsin Organic Synthesis, Greene T. W. and Wuts P. G. M., ed. John Wiley andSons, 1991, and in Protecting Groups, Kocienski P. J., 1994, GeorgThieme Verlag.

When R_(a) represents a hydrogen atom, it is desirable to select, asstarting compound, the amine having the following formula VII, protectedbeforehand on the amino functional group by a protecting group P asdefined above:

NH₂—CR_(b) ²R_(c) ²—CR₃═CR₁R₂  (VII).

The protected amine VII is reacted with a chloride of formula VI asdefined above, preferably in the presence of a base, and then, upondeprotection of the amino functional group, the expected compound offormula III is isolated.

Appropriate bases are for example an organic base chosen fromtriethylamine, diisopropylamine, pyridine and N,N-dimethylaniline or aninorganic base such as NaOH, KOH, NaHCO₃, Na₂CO₃, KHCO₃ and K₂CO₃.

When X represents O and Y represents CR_(b)R_(c), the compounds offormula III are ethers. These ethers are commercially available or areprepared in a manner known per se from commercially available compounds.

The compounds of formula III in which X represents CR_(f)R_(g) and Yrepresents CR_(b)R_(c) are diolefins which are easily accessible to aperson skilled in the art by synthesis or are commercially available.

The compounds of formula III in which X represents NR_(a) where R_(a)represents H or alkyl; R₁=R₆; R₂=R₅; R₃=R₄; and Y₁=Y₂=SiR_(d)R_(e) maybe prepared by the action of an amine R_(a)—NH₂ with two equivalents ofa silyl chloride of formula:

ClSiR_(d)R_(e)—CR₃═CR₁R₂

in which R_(e), R_(d), R₁, R₂ and R₃ are as defined above.

The compounds of formula III in which X represents NR_(a), R_(a) beingas defined above in formula I; Y₁=Y₂=SiR_(d)R_(e) where R_(e) is asdefined above in formula I; the two groups R_(d) together form thechain:

—NR_(a)—(SiR_(e)R_(d) ⁰—NR_(a))_(n)—

in which R_(a) and R_(e) are as defined above; n represents an integerfrom 1 to 3; R_(d) ⁰ represents —CR₃═CR₁R₂; R₁=R₆; R₂=R₅ and R₃=R₄, maybe prepared by reacting the amine R_(a)—NH₂ with the silyl chloride offormula:

Cl₂SiR_(e)—CR₃═CR₁R₂

in which R_(e), R₁, R₂ and R₃ are as defined above.

The compounds of formula III in which X represents O, and Y₁ and Y₂represent SiR_(d)R_(e) are linear, branched or cyclic siloxanes whichare commercially available or whose preparation is possible fromcommercial compounds, using conventional state of the art methods.Examples of preferred siloxanes of formula III are ViMe₂SiOSiMe₂Vi and(MeViSiO)₃, the second formula representing a cyclosiloxane in which Virepresents vinyl.

In the case of the symmetric compounds of formula III, that is to saythose for which R₁=R₆; R₂=R₅; R₃=R₄ and Y₁=Y₂, one of the variants offollowing synthesis may be used.

(Variant a): For the preparation of said symmetric siloxanes of formulaIII for which R₁, R₂, R₃, R_(d) and R_(e) are independently chosen fromalkyl, aryl, alkenyl and alkynyl, a silyl chloride of formulaCl₂SiR_(d)R_(e) may be reacted with an organometallic compound offormula:

CR₁R₂═CR₃—Mg-Hal

where R₁, R₂, R₃ are as defined above and Hal represents a halogen atomunder the usual reaction conditions using magnesium compounds.

(Variant b): For the preparation of said symmetric siloxanes of formulaIII for which R₁=R₂=R₃=H and R_(c), R_(d) are chosen from alkenyl,alkynyl, aryl and alkyl, a silyl chloride of formula Cl₂SiR_(d)—CH═CH₂may be reacted with an organometallic compound of formula:

Re—Mg-hal

in which R_(e) is as defined above and hal represents halogen.

For the use of this variant, persons skilled in the art may refer to J.Gen. Chem., USSR, 1977, 47, 1402-1406.

(Variant c): For the preparation of said symmetric siloxanes of formulaIII in which R₁=R₃=H and R₂ represents alkyl, a siloxane of formula:

H—SiR_(d)R_(e)—O—SiR_(d)R_(e)H

can be reacted with two equivalents of an acetylene hydrocarbon offormula H—C≡C—R₂ in which R₂ is as defined above.

Cyclic siloxanes of formula III are described in U.S. Pat. No.4,593,084.

The compounds of formula III in which X represents CR_(f)R_(g) and Y₁and Y₂ independently represent —SiR_(d)R_(e) may be prepared using amethod similar to one of those described in:

J. of Organometallic Chemistry, 1996, vol. 521, 99-107 (which method ismore particularly appropriate for the preparation of the symmetriccompounds of formula III in which Y₁=Y₂; R_(f)=R_(g)=H; R_(d), R_(e)represent alkyl or aryl optionally substituted with alkyl; R₃ representsa hydrogen atom; alkyl; or aryl which is optionally substituted; and R₁,R₂ are chosen from a hydrogen atom and alkyl);

J. of Organometallic Chemistry, 1997, vol. 545-546, 185-189 (whichmethod is more particularly appropriate for the preparation of symmetriccompounds of formula III in which Y₁=Y₂; R_(f)=R_(g)=Cl or Br; R_(d) andR_(e) represent alkyl; R₁=R₂=R₃=a hydrogen atom);

J. Chem. Soc., Perkin Trans II, 1987, p.381 (which method is moreparticularly appropriate for the preparation of the symmetric compoundsof formula III in which Y₁=Y₂; R_(f)=R_(g)=SiG₁G₂G₃; R_(d) and R_(e)represent alkyl; R₁=R₂=R₃=a hydrogen atom).

The carbenes of formula II.1 and II.2 may be prepared by deprotonationof imidazolium salts, of tetrazolium salts, of triazolium salts or ofpyrazolium salts according to the case, under the action of a base.

These reactions may be schematically represented as follows:

In these reaction schemes, T₁, T₂, T₃, T₄, A and B are as defined abovefor formula I and X⁻ represents an anion.

The nature of the anion X⁻ is not critical according to the invention.The anion X⁻ is the anion derived from an organic or inorganic Bronstedacid (protic acid). Usually, the anion X⁻ is derived from an acid havinga pKa of less than 6. Preferably, X⁻ is derived from an acid having apKa of less than 4, even better of less than 2. The pKa values inquestion here are the pKa values for acids as measured in water.

Examples of acids are carboxylic acids of formula G_(o)—COOH in whichG_(o) represents alkyl, and for example (C₁-C₂₂)alkyl; or alternativelyaryl, and for example (C₆-C₁₈)aryl optionally substituted with one ormore alkyls, preferably one or more (C₁-C₆)alkyl; the sulfonic acids offormula G_(o)—SO₃H in which G_(o) is as defined above; and thephosphonic acids of formula G_(o)—PO₃H in which G_(o) is as definedabove; other acids are HF, HCl, HBr, HI, H₂SO₄, H₃PO₄ and HClO₄.

Preferred examples of carboxylic acids are acetic acid, benzoic acid andstearic acid. By way of preferred sulfonic acid, there will be mentionedbenzenesulfonic acid and by way of preferred phosphonic acid, there willbe mentioned phenylphosphonic acid.

According to the invention, the anions X⁻ derived from HF, HCl, HBr, HI,H₂SO₄ and H₃PO₄ acids are more particularly preferred.

Thus, particularly preferred anions X⁻, according to the invention, arehalide, sulphate, hydrogen sulphate, phosphate, hydrogen phosphate anddihydrogen phosphate anions. There may also be mentioned, as anions,tetrafluoroborates and hexaphenyl phosphate.

The bases which may be used for the deprotonation of the salts offormulae VIII.1 and VIII.2 are strong bases chosen from alkali metalhydrides, alkali metal hydroxides, alkali metal carboxylates, alkalimetal alcoholates and alkali metal amides.

Examples of an appropriate base are therefore sodium hydride, potassiumhydroxide, sodium methoxide, potassium tert-butoxide, lithiumdiisopropylamide and mixtures thereof.

The deprotonation reaction is preferably carried out in a solventcapable of dissolving the starting salt of formula VIII.1 or VIII.2, aswell as the other reagents.

The nature of the solvent also depends on the strength of the base.Specifically in the case of a strong base and of particularly reactivestarting salts, it may be necessary to carry out the procedure at lowtemperature.

Generally, the reaction temperature is between 40° C. and −78° C.,preferably between 30 and −50° C., even better between 25 and −40° C.,for example between 20 and −30° C.

Solvents which can be used in the method for preparing carbenes arecyclic or noncyclic ethers such as diethyl ether, diisopropyl ether,tetrahydrofuran, dioxane, dimethoxyethane or dimethyl ether ofdiethylene glycol.

Other solvents which can be used are dimethyl sulfoxide,dimethylformamide, dimethylacetamide, hexamethylphosphorylamide:[(CH₃)₂N]₃PO and hexamethylphosphoramide [(CH₃)₂N]₃P.

The carbenes of formula II.1 in which A and B both represent a carbonatom may also be prepared by reducing the corresponding thiones offormula IX:

This reaction was described by N. Kuhn in Synthesis, 1993, 561.Preferably, the reduction is carried out in an ether or amide typesolvent, as defined above, at a temperature of between 50 and 150° C.,in the presence of potassium.

The starting salts of formula VIII.1 and VIII.2 may, for their part,prepared by reacting the corresponding imidazoles, pyrazoles, triazolesand tetrazoles with an appropriate acid.

The nature of the anion X⁻ in the salts of formula VIII.1 and VIII.2depends on the acid used at this stage. The acids which can be used arefor example those listed above and from which X⁻ is derived.

Another method for synthesizing the salts of formula VIII.1 in whichA=B=C is described in U.S. Pat. No. 5,077,414.

This method comprises the reaction of an α-dicarbonyl compound X offormula:

in which T₃ and T₄ are as defined above with HCHO and two amines offormulae T₁—NH₂ and T₂—NH₂ in the presence of an appropriate acid.

Other methods for preparing the salts of formulae VIII.1 and VIII.2 areproposed in Chem. Eur. J. 1996, 2, No. 12, pages 1627-1636 and Angew.Chem. Int. Ed. Engl. 1997, 36, 2162-2187.

The compounds of formula IX may be prepared by condensing an appropriatethiourea of formula XI:

with an α-hydroxyketone of formula XII:

in which T₁, T₂, T₃ and T₄ are as defined above. Appropriate operatingconditions are in particular described by N. Kuhn in Synthesis, 1993,561.

According to a particularly preferred embodiment of the invention, themetal complex of the invention has the formula:

in which L is as defined above.

A simple method for preparing this complex consists in reacting thecarbene L with the Karstedt catalyst having the average formulaPt₂[ViMe₂Si—O—SiMe₂Vi]₃ in which Vi represents the vinyl radical.

This reaction may be carried out in bulk or in a solvent.

Examples of appropriate solvents are cyclic or noncyclic ethers such asdiethyl ether, diisopropyl ether, tetrahydrofuran, dioxane,dimethoxyethane or dimethyl ether of diethylene glycol; amides such asdimethylformamide, or dimethylacetamide; aromatic hydrocarbons (such astoluene, xylenes and more particularly toluene); and aliphatic alcoholsof the (C₁-C₄)alkanol type (such as ethanol or isopropanol).

Advantageously, the reaction is carried out in an ether, and preferablyin tetrahydrofuran.

The reaction temperature usually varies between 10 and 50° C.,preferably between 15 and 35° C., very preferably between 20 and 25° C.

It is desirable to carry out the procedure in the presence of a slightexcess of carbene relative to the platinum. Thus, the molar ratio of thecarbene L to the platinum generally varies between 1 and 1.3, preferablybetween 1 and 1.1.

A simple way of proceeding consists in pouring, at the appropriatetemperature, a carbene solution in a solvent, into a reactor containinga solution of the Karstedt catalyst in this same solvent.

The molarity of the solutions of the carbene and of the catalyst is notcritical according to the invention.

According to another of its aspects, the invention relates to acatalytic composition comprising, as active substance, one or more metalcomplexes according to the invention.

The complexes of formula I of the invention can be used as catalysts forthe hydrosilylation reactions. The catalysts of the invention allowhomogeneous catalysis of the reaction.

The expression hydrosilylation reaction is understood to mean, accordingto the invention, the reaction of a compound having an ethylene doublebond or having an acetylene triple bond (unsaturated compound) with acompound having at least one unit

in order to form a C—Si bond.

The hydrosilylation reaction may be schematically represented asfollows, in the case of a compound having an ethylene double bond:

and, in the case of a compound having an acetylene triple bond:

The compounds having an ethylene double bond may comprise one or moredouble bonds and from 2 to 40 carbon atoms. These compounds may bealiphatic hydrocarbons having a linear or branched hydrocarbon chain, oralternatively cyclic hydrocarbons, said cyclic or aliphatic hydrocarbonsoptionally carrying one or more substituents of (C₆-C₁₈)aryl typeoptionally substituted with (C₁-C₆)alkyl. The double bonds are generallyterminal. Preferably, the compound having an ethylene double bond has asingle double bond.

Examples of olefins are ethylene, propylene, 1-butylene, 1-pentene,2-methyl-1-butene, 1-hexene, 1-heptene, 1-octene, 3-ethyl-1-hexene,1-decene, 4,4-dimethyl-1-nonene, vinylcyclohexene, styrene and2-vinylnaphthalene.

The compounds having an acetylene triple bond may comprise one or moretriple bonds and from 2 to 40 carbon atoms. These compounds aregenerally aliphatic hydrocarbons having a linear or branched hydrocarbonchain, optionally substituted with (C₃-C₁₀)cycloalkyl (which cycloalkylmay optionally carry one or more (C₁-C₆)alkyl) and/or with (C₆-C₁₀)aryl(which aryl may optionally carry one or more (C₁-C₆)alkyl). Preferably,the compounds containing an acetylene triple bond have a single triplebond. The triple bonds are generally terminal. Examples thereof are:ethynyl, 2-propynyl, 1-propynyl and 2-penten-4-ynyl.

The hydrosilylation of compounds having both one or more ethylene doublebonds and one or more acetylene triple bonds can also be envisaged inthe context of the invention.

Under the operating conditions normally prescribed in the literature forhydrosilylation reactions, the formation of two types of by-products ofthe hydrosilylation reaction are observed, namely the products ofisomerization and the products of hydrogenation. The products ofisomerization result from the isomerization of double bonds. Theproducts of hydrogenation result from the hydrogenation of double andtriple bonds.

Surprisingly, when the hydrosilylation is carried out using the metalcomplexes of the invention as catalyst, the formation of theseby-products is greatly limited. More particularly, a high reduction inthe level of isomers formed is observed.

The hydrosilylation reaction may be carried out in a solvent or in theabsence of solvent. As a variant, one of the reagents can play the roleof solvent: for example the compound having an ethylene double bond orhaving an acetylene triple bond.

Appropriate solvents are solvents which are miscible with the compoundcontaining an Si—H unit.

Under the hydrosilylation reaction conditions, the catalyst complex ofthe invention should be solubilized in the reaction medium.

According to a preferred embodiment of the invention, the reactionmedium for the reaction for preparing the catalyst complex is used as itis or after dilution, without intermediate isolation.

The compound containing an Si—H unit may be a silicon hydride of formulaXIII:

in which:

X is a radical comprising a heteroatom such as O, Si, a halogen atom orthe carbon atom of an aliphatic or aromatic group;

R is a hydrogen atom, an alkyl group, an aryl group, a cycloalkyl group,an alkoxy group, an aryloxy group or a cycloalkoxy group;

a is an integer from 0 to 3.

It should be understood that, according to the invention, the aliphatic,aromatic, alkyl, aryl, cycloalkyl, alkoxy, aryloxy or cycloalkoxy groupsmay be substituted or otherwise. The nature of the substituents isdefined so as not to give rise to side reactions during thehydrosilylation reaction.

Appropriate examples of silane are HSi(OC₂H₅)₃ and HSi(C₂H₅)₃.

The compound containing an Si—H unit may be a siloxane of formula XIV:

in which P₁ to P₅ are independently chosen from alkyl, aryl, alkoxy,aryloxy, arylalkyl or arylalkoxy which are optionally substituted, itbeing possible for P₃, P₄ and/or P₅ to also represent a hydrogen atom.

Preferably, P₁ to P₅ are independently chosen from a (C₁-C₂₂)alkyl,preferably (C₁-C₁₀)alkyl, group; a (C₆-C₁₀)aryl group optionallysubstituted with one or more (C₁-C₁₀)alkyl and/or (C₁-C₁₀)alkoxy; a(C₁-C₂₂)alkoxy, preferably (C₁-C₁₀)alkoxy, group; a (C₆-C₁₀)aryloxygroup in which the aryl portion is optionally substituted with(C₁-C₆)alkyl and/or (C₁-C₆)alkoxy; a (C₆-C₁₀)aryl(C₁-C₁₀)alkyl group inwhich the aryl portion is optionally substituted with (C₁-C₆)alkyland/or (C₁-C₆)alkoxy; or alternatively a (C₆-C₁₀)aryl-(C₁-C₁₀)alkoxygroup in which the aryl portion is optionally substituted with(C₁-C₆)alkyl and/or (C₁-C₆)alkoxy.

The compound having an Si—H unit may be a polymer of polyhydrogensiloxane type. Other appropriate polymers and copolymers are thepolyhydrosilanes comprising a large number of recurring units containingSi—H bonds.

Preferably, the polymers which can be used have recurring units offormula:

in which X is a radical comprising a heteroatom such as O, Si or thecarbon atom of an aliphatic or aromatic group; and R₀ is a hydrogen atomor an organic group chosen from alkyl, aryl, cycloalkyl, alkoxy, aryloxyor cycloalkoxy. By way of examples, there may be mentioned thepolyhydrosiloxanes of formula:

in which R₇ to R₁₃ are independently a hydrogen atom or an organicgroup. Preferably, R₇, R₅, R₉, R₁₀, R₁₁, R₁₂ and R₁₃ are chosen from ahydrogen atom, an alkyl, aryl, cycloalkyl, alkoxy, aryloxy andcycloalkoxy group;

n is an integer at least equal to 1 and preferably at least equal to 10and, even better, between 10 and 100.

Appropriate polymers are polymethyl hydrogen siloxane,polydimethylsiloxane having a terminal —SiH group, methyl hydrogendimethylsiloxane copolymers, methyl hydrogen methyloctylsiloxanecopolymers and methyl hydrogen cyclosiloxane polymers.

In general, the polymers which can be used in the reaction have a meanmolecular mass of 300 or more and preferably of between 300 and 10,000(g/mol).

Examples of silicon hydrides are described in U.S. Pat. No. 5,359,113.

Examples of solvents which can be used for the hydrosilylation are inparticular the aliphatic hydrocarbons (such as pentane, hexane, heptane,pentamethylheptane or the fractions from the distillation of petroleum);aromatic hydrocarbons (such as benzene, toluene and xylenes:ortho-xylene, para-xylene and meta-xylene); halogenated aliphatic oraromatic hydrocarbons (such as tetrachloroethylene); or ethers (such astetrahydrofuran or dioxane).

The hydrosilylation reaction may be carried out at a temperature ofbetween 15° C. and 300° C., for example between 20 and 240° C., evenbetter between 70 and 200° C., in particular between 50 and 140° C.,most preferably between 50 and 100° C.

The relative quantity of unsaturated compound and of compound containingan Si—H unit may be controlled so as to ensure the reaction of all theunsaturations with Si—H bonds.

It is nevertheless preferable to carry out the procedure in the presenceof a molar excess of unsaturation.

The molar ratio of the unsaturations to the Si—H bonds generally variesbetween 1:100 and 10:1.

The concentration of unsaturated compound in the reaction medium isbetween 2 and 50% by weight.

According to the invention, the hydrosilylation reaction is carried outin the presence of a catalytic quantity of one or more complexesaccording to the invention. The expression catalytic quantity isunderstood to mean less than one molar equivalent of platinum relativeto the quantity of unsaturations present in the reaction medium.

In general, it is sufficient to introduce into the reaction medium lessthan 1000 ppm, preferably less than 100 ppm, even better less than 50ppm of platinum calculated relative to the total mass of the unsaturatedcompound and of the compound containing Si—H units.

According to a preferred embodiment of the invention, the unsaturatedcompound, the catalyst and the solvent are placed, with stirring, in areactor. The whole is heated to the desired temperature and the compoundcontaining the unit

is introduced, with stirring.

The invention is illustrated in the text which follows in the light ofthe following examples.

EXAMPLE 1 1—Preparation of the Carbene of Formula

(cf. Chem. Eur. J. 1996, 2, 1627).

For this reaction, all the glassware used is dried in an oven at 150° C.overnight and then cooled under argon.

The THF is distilled over sodium/benzophenone just before use.

A 100 ml three-necked flask is loaded with 2.70 g (10 mmol) of1,3-dicyclohexylimidazolinium chloride and then purged with an argonstream before being suspended in 20 ml of THF. About 50 ml of ammoniaare then condensed at 78° C. in the three-necked flask, causing partialdissolution of the salt. The acetone/dry ice bath is removed and 270 mgof NaH at 95% (10.7 mmol-1.07 eq.) are slowly added using asolid-charging vessel. Each addition of NaH is followed by a highgaseous emission (H₂) and the salt in suspension gradually dissolves.The reaction mixture is stirred for 1 h 30 min at the reflux temperatureof the solvent. The ammonia is then evaporated and a pale yellowsolution is obtained as well as a solid in suspension (NaCl). Thissolution, whose carbene concentration is 0.5M in THF, is usedimmediately for the preparation of the complexes.

2—Preparation of the Platinum Complex of Formula

A Karstedt solution containing 10% by weight of platinum (that is 1.52mmol of platinum) is prepared in accordance with the procedure describedin U.S. Pat. No. 3,775,452.

To 3 g of this solution, kept stirred and diluted in 10 ml oftetrahydrofuran there are added dropwise, using a dropping funnel, 3.2ml of a 0.5M solution of the carbene of formula:

in tetrahydrofuran. The addition is complete after 10 minutes. Thereaction mixture is then stirred for 50 minutes at room temperature.Where appropriate, the light insoluble material is filtered and thereaction mixture is concentrated under vacuum.

After concentration, a slightly yellow viscous residue is obtained.Within a few hours, an abundant white solid precipitates from theresidual divinyltetramethyldisiloxane. It is filtered, washed with a fewmilliliters of hexamethyldisilazane, and then of pentane. 570 mg (60%yield) of an analytically pure white powder are thus obtained.

A fraction of this powder is recrystallized from adichloromethane/absolute ethanol mixture. The resultant crystals areanalyzed by X-ray diffraction. The analysis confirms the structure ofthe complex obtained.

EXAMPLE 2 1—Preparation of the Carbene of Formula

This carbene is prepared using the procedure illustrated in example 1,paragraph 1, except that the 2.7 g (10 mmol) of1,3-dicyclohexylimidazolinium chloride are replaced by 2.3 g (10 mmol)of 1,3-dimethylimidazolinium iodide.

2—Preparation of the Platinum Complex of Formula

This complex is prepared using the procedure of example 1, except thatthe carbene used as starting material has the formula:

After concentration, a yellow paste is obtained. It is filtered andabundantly washed with hot pentane. A whitish solid is isolated (35%yield), which is recrystallized from ethanol. The resulting crystals areanalyzed by X-ray diffraction. The analysis confirms the structure ofthe complex obtained.

EXAMPLE 3 Hydrosilylation of oct-1-ene by the Action of(CH₃)₃Si—O—Si(CH₃)(H)—OSi(CH₃)₃

5 g (45 mmol) of oct-1-ene, 10 g (1 equivalent of SiH units relative tooct-1-ene) of (CH₃)₃SiO—Si(CH₃)(H)—OSi(CH₃)₃, 5 g of dodecane (used asinternal standard for analysis by gas chromatography) and ortho-xylenein sufficient quantity so as to ensure a 0.5M concentration of silylatedreagent and of oct-1-ene, are placed in a 250 ml three-necked reactorequipped with a condenser, with magnetic stirring and with athermometric sheath, and heated using an oil bath. The whole is heatedto 70° C. and kept stirred.

Next, a solution of the catalyst in dichloromethane containing 30 ppm ofplatinum calculated relative to the total quantity of silylatedderivative and of oct-1-ene, is added to the preceding mixture, all atonce.

The progress of the reaction is monitored by gas chromatography (GC).

The successive samples analyzed by GC are eluted beforehand on a columnof activated charcoal.

The preceding hydrosilylation reaction is carried out under the sameconditions starting with three different catalysts:

the Karstedt catalyst prepared according to U.S. Pat. No. 3,775,452;

the catalyst prepared in example 1;

the catalyst prepared in example 2.

The results obtained, expressed as rate of conversion (τ) of Si—H bondsin the silylated derivative and as percentage of isomerization (p) arereported in the following table.

TABLE Catalyst τ (%) p (%) Karstedt 80 17 Example 1 82 4.5 Example 2 853.7

It is observed that the catalysts of the invention lead to much lowerpercentages of isomerization (by a factor of 3).

EXAMPLE 4

In this example, the hydrosilylation of 1-octene is carried out by theaction of (CH₃)₃SiO—Si(H)(CH₃)—OSi(CH₃)₃ in the presence of the complexof example 2 as catalyst.

The quantities of reagents and of catalyst brought into contact are thesame as in example 3. Only the manner of proceeding was modified. 5 g(45 mmol) of oct-1-ene, 5 g of dodecane and the solution of the catalystin dichloromethane (which contains 30 ppm of platinum calculatedrelative to the total quantity of silylated derivative and of oct-1-ene)are placed in a 100 ml three-necked flask equipped with magneticstirring and a condenser, and heated using an oil bath. This solution iskept stirred and heated to 70° C. Next, 10 g (1 equivalent of Si—H unitsrelative to oct-1-ene) of (CH₃)₃SiO—Si(CH₃)(H)—OSi(CH₃)₃ are introduceddropwise into the reaction medium. The progress of the reaction ismonitored by gas chromatography. A rate of conversion of Si—H bonds inthe silylated derivative of 96% and a percentage of isomerization of1.5% are obtained.

What is claimed is:
 1. A metal complex of formula I

in which: M represents a metal having an oxidation number 0 chosen fromthe group 8 metals in the Periodic Table as published in the Handbook ofChemistry and Physics, 65th Edition, 1984-1985; X represents O, NR_(a)or CR_(f)R_(g); Y₁ and Y₂ represent, independently of each other,CR_(b)R_(c) or SiR_(d)R_(e); R₁, R_(w), R₅ and R₆, which are identicalor different, are chosen from a hydrogen atom, an alkyl group and anaryl group optionally substituted with alkyl; R₃, R₄, R_(a), R_(b),R_(c) are independently chosen from a hydrogen atom; an alkyl group; anacyl group; an aryl group optionally substituted with alkyl; acycloalkyl group optionally substituted with alkyl; and an arylalkylgroup in which the aryl portion is optionally substituted with alkyl;R_(d) and R_(e) are independently chosen from alkenyl; alkynyl; alkyl;alkoxy; acyl; aryl optionally substituted with alkyl; cycloalkyloptionally substituted with alkyl; and arylalkyl in which the arylportion is optionally substituted with alkyl; or alternatively when Y₁and Y₂ independently represent SiR_(d)R_(e), two R_(d) groups linked totwo separate silicon atoms together form a chain of formula:

in which n is an integer from 1 to 3; X is as defined above; R and R′,which are identical or different, take any one of the meanings givenabove for R_(e), it being understood that when N is 2 or 3, a singlesilicon atom of said chain may be substituted with one or two alkenyl oralkynyl groups; or alternatively when Y₁ and Y₂ independently representSiR_(d)R_(e), two R_(d) groups linked to separate silicon atoms togetherform a saturated hydrocarbon chain, the two R_(b) groups together withsaid silicon atoms and X forming a 6- to 10-membered ring; oralternatively when Y₁ and Y₂ independently represent CR_(b)R_(c), twoR_(b) groups linked to separate carbon atoms together form a saturatedhydrocarbon chain, the two R_(b) groups together with the carbon atomscarrying them and X form a 6- to 10-membered ring; and R_(f) and R_(g)represent, independently of each other, a hydrogen atom; an alkyl group;an acyl group; an aryl group optionally substituted with alkyl; acycloalkyl group optionally substituted with alkyl; an arylalkyl groupin which the aryl portion is optionally substituted with alkyl; ahalogen atom; an alkenyl group; an alkynyl group; or a group SiG₁G_(w)G₃where G₁, G₂ and G₃ are, independently of each other, alkyl; alkoxy;aryl optionally substituted with alkyl or alkoxy; or arylalkyl in whichthe aryl portion is optionally substituted with alkyl or alkoxy; Lrepresents a carbene of formula II.1 or II.2:

in which: A and B independently represent C or N, it being understoodthat when A represents N, then T₄ represents nothing and when Brepresents N, then T₃ represents nothing; T₃ and T₄ independentlyrepresent a hydrogen atom; an alkyl group; a cycloalkyl group optionallysubstituted with alkyl or alkoxy; an aryl group optionally substitutedwith alkyl or alkoxy; an alkenyl group; an alkynyl group; or anarylalkyl group in which the aryl portion is optionally substituted withalkyl or alkoxy; T₁ and T₂ independently represent an alkyl group; analkyl group which is perfluorinated or optionally substituted with aperfluoroalkyl group; a cycloalkyl group optionally substituted withalkyl or alkoxy; an aryl group optionally substituted with alkyl oralkoxy; an alkenyl group; an alkynyl group; or an arylalkyl group inwhich the aryl portion is optionally substituted with alkyl or alkoxy;or alternatively the substituents T₁, T₂, T₃ and T₄, may form in pairs,when they are located on two adjacent summits in the formulae II.1 andII.2, a saturated or unsaturated hydrocarbon chain.
 2. A metal complexof formula I

in which: M represents a metal having an oxidation number 0 chosen fromthe group 8 metals in the Periodic Table as published in the Handbook ofChemistry and Physics, 65th Edition, 1984-1 985; X represents O, NR_(a)or CR_(f)R_(g); Y₁ and Y₂ represent, independently of each other,CR_(b)R_(c) or SiR_(d)R_(e); R₁, R_(w), R₅ and R₆, which are identicalor different, are chosen from a hydrogen atom, an alkyl group and anaryl group optionally substituted with alkyl; R₃, R₄, R_(a), R_(b),R_(c) are independently chosen from a hydrogen atom; an alkyl group; anacyl group; an aryl group optionally substituted with alkyl; acycloalkyl group optionally substituted with alkyl; and an arylalkylgroup in which the aryl portion is optionally substituted with alkyl;R_(d) and R_(e) are independently chosen from alkenyl; alkynyl; alkyl;alkoxy; acyl; aryl optionally substituted with alkyl; cycloalkyloptionally substituted with alkyl; and arylalkyl in which the arylportion is optionally substituted with alkyl; or alternatively when Y₁and Y₂ independently represent SiR_(d)R_(e), two R_(d) groups linked totwo separate silicon atoms together form a chain of formula:

in which n is an integer from 1 to 3; X is as defined above; R and R′,which are identical or different, take any one of the meanings givenabove for R_(e), it being understood that when N is 2 or 3, a singlesilicon atom of said chain may be substituted with one or two alkenyl oralkynyl groups; or alternatively when Y₁ and Y₂ independently representSiR_(d)R_(e), two R_(d) groups linked to separate silicon atoms togetherform a saturated hydrocarbon chain, the two R_(b) groups together withsaid silicon atoms and X forming a 6- to 10-membered ring; oralternatively when Y₁ and Y₂ independently represent CR_(b)R_(c), twoR_(b) groups linked to separate carbon atoms together form a saturatedhydrocarbon chain, the two R_(b) groups together with the carbon atomscarrying them and X form a 6- to 10-membered ring; and R_(f) and R_(g)represent, independently of each other, a hydrogen atom; an alkyl group;an acyl group; an aryl group optionally substituted with alkyl; acycloalkyl group optionally substituted with alkyl; an arylalkyl groupin which the aryl portion is optionally substituted with alkyl; ahalogen atom; an alkenyl group; an alkynyl group; or a group SiG₁G_(w)G₃where G₁, G₂ and G₃ are, independently of each other, alkyl; alkoxy;aryl optionally substituted with alkyl or alkoxy; or arylalkyl in whichthe aryl portion is optionally substituted with alkyl or alkoxy; Lrepresents a carbene of formula II.1 or II.2:

in which: A and B independently represent C or N, it being understoodthat when A represents N, then T₄ represents nothing and when Brepresents N, then T₃ represents nothing; T₃ and T₄ independentlyrepresent a hydrogen atom; an alkyl group; a cycloalkyl group optionallysubstituted with alkyl or alkoxy; an aryl group optionally substitutedwith alkyl or alkoxy; an alkenyl group; an alkynyl group; or anarylalkyl group in which the aryl portion is optionally substituted withalkyl or alkoxy; T₁ and T₂ independently represent an alkyl group; analkyl group which is perfluorinated or optionally substituted with aperfluoroalkyl group; a cycloalkyl group optionally substituted withalkyl or alkoxy; an aryl group optionally substituted with alkyl oralkoxy; an alkenyl group; an alkynyl group; or an arylalkyl group inwhich the aryl portion is optionally substituted with alkyl or alkoxy;or alternatively the substituents T₁, T₂, T₃ and T₄, may form in pairs,when they are located on two adjacent summits in the formulae II.1 andII.2, a saturated or unsaturated hydrocarbon chain wherein X representsO; Y₁ and Y₂ represent, independently of each other, SiR_(d)R_(e). 3.The metal complex as claimed in claim 1, in which L represents a carbeneof formula II.1.
 4. The metal complex as claimed in claim 1, wherein R₁,R₂, R₅ and R₆ are hydrogen atoms.
 5. The metal complex as claimed inclaim 1, wherein R₃ and R₄ represent a hydrogen atom; an alkyl group; anaryl group optionally substituted with alkyl; or a cycloalkyl groupoptionally substituted with alkyl.
 6. A metal complex of formula I

in which: M represents a metal having an oxidation number 0 chosen fromthe group 8 metals in the Periodic Table as published in the Handbook ofChemistry and Physics, 65th Edition, 1984-1985; X represents O, NR_(a)or CR_(f)R_(g); Y₁ and Y₂ represent, independently of each other,CR_(b)R_(c) or SiR_(d)R_(e); R₁, R_(w), R₅ and R₆, which are identicalor different, are chosen from a hydrogen atom, an alkyl group and anaryl group optionally substituted with alkyl; R₃, R₄, R_(a), R_(b),R_(c) are independently chosen from a hydrogen atom; an alkyl group; anacyl group; an aryl group optionally substituted with alkyl; acycloalkyl group optionally substituted with alkyl; and an arylalkylgroup in which the aryl portion is optionally substituted with a alkyl;R_(d) and R_(e) are independently chosen from alkenyl; alkynyl; alkyl;alkoxy; acyl; aryl optionally substituted with alkyl; cycloalkyloptionally substituted with alkyl; and arylalkyl in which the arylportion is optionally substituted with alkyl; or alternatively when Y₁and Y₂ independently represent SiR_(d)R_(e), two R_(d) groups linked totwo separate silicon atoms together form a chain of formula:

in which n is an integer from 1 to 3; X is as defined above; R and R′,which are identical or different, take any one of the meanings givenabove for R_(e), it being understood that when N is 2 or 3, a singlesilicon atom of said chain may be substituted with one or two alkenyl oralkynyl groups; or alternatively when Y₁ and Y₂ independently representSiR_(d)R_(e), two R_(d) groups linked to separate silicon atoms togetherform a saturated hydrocarbon chain, the two R_(b) groups together withsaid silicon atoms and X forming a 6- to 10-membered ring; oralternatively when Y₁ and Y₂ independently represent CR_(b)R_(c), twoR_(b) groups linked to separate carbon atoms together form a saturatedhydrocarbon chain, the two R_(b) groups together with the carbon atomscarrying them and X form a 6- to 10-membered ring; and R_(f) and R_(g)represent, independently of each other, a hydrogen atom; an alkyl group;an acyl group; an aryl group optionally substituted with alkyl; acycloalkyl group optionally substituted with alkyl; an arylalkyl groupin which the aryl portion is optionally substituted with alkyl; ahalogen atom; an alkenyl group; an alkynyl group; or a group SiG₁G_(w)G₃where G₁, G₂ and G₃ are, independently of each other, alkyl; alkoxy;aryl optionally substituted with alkyl or alkoxy; or arylalkyl in whichthe aryl portion is optionally substituted with alkyl or alkoxy; Lrepresents a carbene of formula II.1 or II.2:

in which: A and B independently represent C or N, it being understoodthat when A represents N, then T₄ represents nothing and when Brepresents N, then T₃ represents nothing; T₃ and T₄ independentlyrepresent a hydrogen atom; an alkyl group; a cycloalkyl group optionallysubstituted with alkyl or alkoxy; an aryl group optionally substitutedwith alkyl or alkoxy; an alkenyl group; an alkynyl group; or anarylalkyl group in which the aryl portion is optionally substituted withalkyl or alkoxy; T₁ and T₂ independently represent an alkyl group; analkyl group which is perfluorinated or optionally substituted with aperfluoroalkyl group; a cycloalkyl group optionally substituted withalkyl or alkoxy; an aryl group optionally substituted with alkyl oralkoxy; an alkenyl group; an alkynyl group; or an arylalkyl group inwhich the aryl portion is optionally substituted with alkyl or alkoxy;or alternatively the substituents T₁, T₂, T₃ and T₄, may form in pairs,when they are located on two adjacent summits in the formulae II.1 andII.2, a saturated or unsaturated hydrocarbon chain, wherein A and B bothrepresent a carbon atom.
 7. A metal complex of formula I

in which: M represents a metal having an oxidation number 0 chosen fromthe group 8 metals in the Periodic Table as published in the Handbook ofChemistry and Physics, 65th Edition, 1984-1985; X represents O, NR_(a)or CR_(f)R_(g); Y₁ and Y₂ represent, independently of each other,CR_(b)R_(c) or SiR_(d)R_(e); R₁, R_(w), R₅ and R₆, which are identicalor different, are chosen from a hydrogen atom, an alkyl group and anaryl group optionally substituted with alkyl; R₃, R₄, R_(a), R_(b),R_(c) are independently chosen from a hydrogen atom; an alkyl group; anacyl group; an aryl group optionally substituted with alkyl; acycloalkyl group optionally substituted with alkyl; and an arylalkylgroup in which the aryl portion is optionally substituted with alkyl;R_(d) and R_(e) are independently chosen from alkenyl; alkynyl; alkyl;alkoxy; acyl; aryl optionally substituted with alkyl; cycloalkyloptionally substituted with alkyl; and arylalkyl in which the arylportion is optionally substituted with alkyl; or alternatively when Y₁and Y₂ independently represent SiR_(d)R_(e), two R_(d) groups linked totwo separate silicon atoms together form a chain of formula:

in which n is an integer from 1 to 3; X is as defined above; R and R′,which are identical or different, take any one of the meanings givenabove for R_(e), it being understood that when N is 2 or 3, a singlesilicon atom of said chain may be substituted with one or two alkenyl oralkynyl groups; or alternatively when Y₁ and Y₂ independently representSiR_(d)R_(e), two R_(d) groups linked to separate silicon atoms togetherform a saturated hydrocarbon chain, the two R_(b) groups together withsaid silicon atoms and X forming a 6- to 10-membered ring; oralternatively when Y₁ and Y₂ independently represent CR_(b)R_(c), twoR_(b) groups linked to separate carbon atoms together form a saturatedhydrocarbon chain, the two R_(b) groups together with the carbon atomscarrying them and X form a 6- to 10-membered ring; and R_(f) and R_(g)represent, independently of each other, a hydrogen atom; an alkyl group;an acyl group; an aryl group optionally substituted with alkyl; acycloalkyl group optionally substituted with alkyl; an arylalkyl groupin which the aryl portion is optionally substituted with alkyl; ahalogen atom; an alkenyl group; an alkynyl group; or a group SiG₁G_(w)G₃where G₁, G₂ and G₃ are, independently of each other, alkyl; alkoxy;aryl optionally substituted with alkyl or alkoxy; or arylalkyl in whichthe aryl portion is optionally substituted with alkyl or alkoxy; Lrepresents a carbene of formula II.1 or II.2:

in which: A and B independently represent C or N, it being understoodthat when A represents N, then T₄ represents nothing and when Brepresents N, then T₃ represents nothing; T₃ and T₄ independentlyrepresent a hydrogen atom; an alkyl group; a cycloalkyl group optionallysubstituted with alkyl or alkoxy; an aryl group optionally substitutedwith alkyl or alkoxy; an alkenyl group; an alkynyl group; or anarylalkyl group in which the aryl portion is optionally substituted withalkyl or alkoxy; T₁ and T₂ independently represent an alkyl group; analkyl group which is perfluorinated or optionally substituted with aperfluoroalkyl group; a cycloalkyl group optionally substituted withalkyl or alkoxy; an aryl group optionally substituted with alkyl oralkoxy; an alkenyl group; an alkynyl group; or an arylalkyl group inwhich the aryl portion is optionally substituted with alkyl or alkoxy;or alternatively the substituents T₁, T₂, T₃ and T₄, may form in pairs,when they are located on two adjacent summits in the formulae II.1 andII.2, a saturated or unsaturated hydrocarbon chain, wherein T₃ and T₄represent a hydrogen atom.
 8. A metal complex of formula I

in which: M represents a metal having an oxidation number 0 chosen fromthe group 8 metals in the Periodic Table as published in the Handbook ofChemistry and Physics, 65th Edition, 1984-1985; X represents O, NR_(a)or CR_(f)R_(g); Y₁ and Y₂ represent, independently of each other,CR_(b)R_(c) or SiR_(d)R_(e); R₁, R_(w), R₅ and R₆, which are identicalor different, are chosen from a hydrogen atom, an alkyl group and anaryl group optionally substituted with alkyl; R₃, R₄, R_(a), R_(b),R_(c) are independently chosen from a hydrogen atom; an alkyl group; anacyl group; an aryl group optionally substituted with alkyl; acycloalkyl group optionally substituted with alkyl; and an arylalkylgroup in which the aryl portion is optionally substituted with alkyl;R_(d) and R_(e) are independently chosen from alkenyl; alkynyl; alkyl;alkoxy; acyl; aryl optionally substituted with alkyl; cycloalkyloptionally substituted with alkyl; and arylalkyl in which the arylportion is optionally substituted with alkyl; or alternatively when Y₁and Y₂ independently represent SiR_(d)R_(e), two R_(d) groups linked totwo separate silicon atoms together form a chain of formula:

in which n is an integer from 1 to 3; X is as defined above; R and R′,which are identical or different, take any one of the meanings givenabove for R_(e), it being understood that when N is 2 or 3, a singlesilicon atom of said chain may be substituted with one or two alkenyl oralkynyl groups; or alternatively when Y₁ and Y₂ independently representSiR_(d)R_(e), two R_(d) groups linked to separate silicon atoms togetherform a saturated hydrocarbon chain, the two R_(b) groups together withsaid silicon atoms and X forming a 6-to 10-membered ring; oralternatively when Y₁ and Y₂ independently represent CR_(b)R_(c), twoR_(b) groups linked to separate carbon atoms together form a saturatedhydrocarbon chain, the two R_(b) groups together with the carbon atomscarrying them and X form a 6- to 10-membered ring; and R_(f) and R_(g)represent, independently of each other, a hydrogen atom; an alkyl group;an acyl group; an aryl group optionally substituted with alkyl; acycloalkyl group optionally substituted with alkyl; an arylalkyl groupin which the aryl portion is optionally substituted with alkyl; ahalogen atom; an alkenyl group; an alkynyl group; or a group SiG₁G_(w)G₃where G₁, G₂ and G₃ are, independently of each other, alkyl; alkoxy;aryl optionally substituted with alkyl or alkoxy; or arylalkyl in whichthe aryl portion is optionally substituted with alkyl or alkoxy; Lrepresents a carbene of formula II.1 or II.2:

in which: A and B independently represent C or N, it being understoodthat when A represents N, then T₄ represents nothing and when Brepresents N, then T₃ represents nothing; T₃ and T₄ independentlyrepresent a hydrogen atom; an alkyl group; a cycloalkyl group optionallysubstituted with alkyl or alkoxy; an aryl group optionally substitutedwith alkyl or alkoxy; an alkenyl group; an alkynyl group; or anarylalkyl group in which the aryl portion is optionally substituted withalkyl or alkoxy; T₁ and T₂ independently represent an alkyl group; analkyl group which is perfluorinated or optionally substituted with aperfluoroalkyl group; a cycloalkyl group optionally substituted withalkyl or alkoxy; an aryl group optionally substituted with alkyl oralkoxy; an alkenyl group; an alkynyl group; or an arylalkyl group inwhich the aryl portion is optionally substituted with alkyl or alkoxy;or alternatively the substituents T₁, T₂, T₃ and T₄, may form in pairs,when they are located on two adjacent summits in the formulae II.1 andII.2, a saturated or unsaturated hydrocarbon chain, wherein T₁ and T₂,which are identical or different, represent (C₁-C₈)alkyl or(C₃-C₈)cycloalkyl; or alternatively R₃ and R₄, which are identical ordifferent, represent (C₁-C₈)alkyl or (C₃-C₈)cycloalkyl; or stillalternatively T₁, T₂, R₃ and R₄, which are identical or different,represent (C₁-C₈)alkyl or (C₃-C₈)cycloalkyl.
 9. A metal complex offormula I

in which: M represents a metal having an oxidation number 0 chosen fromthe group 8 metals in the Periodic Table as published in the Handbook ofChemistry and Physics, 65th Edition, 1984-1985; X represents O, NR_(a)or CR_(f)R_(g); Y₁ and Y₂ represent, independently of each other,CR_(b)R_(c) or SiR_(d)R_(e); R₁, R_(w), R₅ and R₆, which are identicalor different, are chosen from a hydrogen atom, an alkyl group and anaryl group optionally substituted with alkyl; R₃, R₄, R_(a), R_(b),R_(c) are independently chosen from a hydrogen atom; an alkyl group; anacyl group; an aryl group optionally substituted with alkyl; acycloalkyl group optionally substituted with alkyl; and an arylalkylgroup in which the aryl portion is optionally substituted with alkyl;R_(d) and R_(e) are independently chosen from alkenyl; alkynyl; alkyl;alkoxy; acyl; aryl optionally substituted with alkyl; cycloalkyloptionally substituted with alkyl; and arylalkyl in which the arylportion is optionally substituted with alkyl; or alternatively when Y₁and Y₂ independently represent SiR_(d)R_(e), two R_(d) groups linked totwo separate silicon atoms together form a chain of formula:

in which n is an integer from 1 to 3; X is as defined above; R and R′,which are identical or different, take any one of the meanings givenabove for R_(e), it being understood that when N is 2 or 3, a singlesilicon atom of said chain may be substituted with one or two alkenyl oralkynyl groups; or alternatively when Y₁ and Y₂ independently representSiR_(d)R_(e), two R_(d) groups linked to separate silicon atoms togetherform a saturated hydrocarbon chain, the two R_(b) groups together withsaid silicon atoms and X forming a 6- to 10-membered ring; oralternatively when Y₁ and Y₂ independently represent CR_(b)R_(c), twoR_(b) groups linked to separate carbon atoms together form a saturatedhydrocarbon chain, the two R_(b) groups together with the carbon atomscarrying them and X form a 6- to 10-membered ring; and R_(f) and R_(g)represent, independently of each other, a hydrogen atom; an alkyl group;an acyl group; an aryl group optionally substituted with alkyl; acycloalkyl group optionally substituted with alkyl; an arylalkyl groupin which the aryl portion is optionally substituted with alkyl; ahalogen atom; an alkenyl group; an alkynyl group; or a group SiG₁G_(w)G₃where G₁, G₂ and G₃ are, independently of each other, alkyl; alkoxy;aryl optionally substituted with alkyl or alkoxy; or arylalkyl in whichthe aryl portion is optionally substituted with alkyl or alkoxy; Lrepresents a carbene of formula II.1 or II.2:

in which: A and B independently represent C or N, it being understoodthat when A represents N, then T₄ represents nothing and when Brepresents N, then T₃ represents nothing; T₃ and T₄ independentlyrepresent a hydrogen atom; an alkyl group; a cycloalkyl group optionallysubstituted with alkyl or alkoxy; an aryl group optionally substitutedwith alkyl or alkoxy; an alkenyl group; an alkynyl group; or anarylalkyl group in which the aryl portion is optionally substituted withalkyl or alkoxy; T₁ and T₂ independently represent an alkyl group; analkyl group which is perfluorinated or optionally substituted with aperfluoroalkyl group; a cycloalkyl group optionally substituted withalkyl or alkoxy; an aryl group optionally substituted with alkyl oralkoxy; an alkenyl group; an alkynyl group; or an arylalkyl group inwhich the aryl portion is optionally substituted with alkyl or alkoxy;or alternatively the substituents T₁, T₂, T₃ and T₄, may form in pairs,when they are located on two adjacent summits in the formulae II.1 andII.2, a saturated or unsaturated hydrocarbon chain, wherein T₁ and T₂are identical and represent (C₃-C₈)cycloalkyl.
 10. A metal complex offormula I

in which: M represents a metal having an oxidation number 0 chosen fromthe group 8 metals in the Periodic Table as published in the Handbook ofChemistry and Physics, 65th Edition, 1984-1985; X represents O, NR_(a)or CR_(f)R_(g); Y₁ and Y₂ represent, independently of each other,CR_(b)R_(c) or SiR_(d)R_(e); R₁, R_(w), R₅ and R₆, which are identicalor different, are chosen from a hydrogen atom, an alkyl group and anaryl group optionally substituted with alkyl; R₃, R₄, R_(a), R_(b),R_(c) are independently chosen from a hydrogen atom; an alkyl group; anacyl group; an aryl group optionally substituted with alkyl; acycloalkyl group optionally substituted with alkyl; and an arylalkylgroup in which the aryl portion is optionally substituted with alkyl;R_(d) and R_(e) are independently chosen from alkenyl; alkynyl; alkyl;alkoxy; acyl; aryl optionally substituted with alkyl; cycloalkyloptionally substituted with alkyl; and arylalkyl in which the arylportion is optionally substituted with alkyl; or alternatively when Y₁and Y₂ independently represent SiR_(d)R_(e), two R_(d) groups linked totwo separate silicon atoms together form a chain of formula:

in which n is an integer from 1 to 3; X is as defined above; R and R′,which are identical or different, take any one of the meanings givenabove for R_(e), it being understood that when N is 2 or 3, a singlesilicon atom of said chain may be substituted with one or two alkenyl oralkynyl groups; or alternatively when Y₁ and Y₂ independently representSiR_(d)R_(e), two R_(d) groups linked to separate silicon atoms togetherform a saturated hydrocarbon chain, the two R_(b) groups together withsaid silicon atoms and X forming a 6- to 10-membered ring; oralternatively when Y₁ and Y₂ independently represent CR_(b)R_(c), twoR_(b) groups linked to separate carbon atoms together form a saturatedhydrocarbon chain, the two R_(b) groups together with the carbon atomscarrying them and X form a 6- to 10-membered ring; and R_(f) and R_(g)represent, independently of each other, a hydrogen atom; an alkyl group;an acyl group; an aryl group optionally substituted with alkyl; acycloalkyl group optionally substituted with alkyl; an arylalkyl groupin which the aryl portion is optionally substituted with alkyl; ahalogen atom; an alkenyl group; an alkynyl group; or a group SiG₁G_(w)G₃where G₁, G₂ and G₃ are, independently of each other, alkyl; alkoxy;aryl optionally substituted with alkyl or alkoxy; or arylalkyl in whichthe aryl portion is optionally substituted with alkyl or alkoxy; Lrepresents a carbene of formula II.1 or II.2:

in which: A and B independently represent C or N, it being understoodthat when A represents N, then T₄ represents nothing and when Brepresents N, then T₃ represents nothing; T₃ and T₄ independentlyrepresent a hydrogen atom; an alkyl group; a cycloalkyl group optionallysubstituted with alkyl or alkoxy; an aryl group optionally substitutedwith alkyl or alkoxy; an alkenyl group; an alkynyl group; or anarylalkyl group in which the aryl portion is optionally substituted withalkyl or alkoxy; T₁ and T₂ independently represent an alkyl group; analkyl group which is perfluorinated or optionally substituted with aperfluoroalkyl group; a cycloalkyl group optionally substituted withalkyl or alkoxy; an aryl group optionally substituted with alkyl oralkoxy; an alkenyl group; an alkynyl group; or an arylalkyl group inwhich the aryl portion is optionally substituted with alkyl or alkoxy;or alternatively the substituents T₁, T₂, T₃ and T₄, may form in pairs,when they are located on two adjacent summits in the formulae II.1 andII.2, a saturated or unsaturated hydrocarbon chain, wherein M is a metalselected from the group consisting of Pt, Pd and Ni.
 11. A metal complexof formula I

in which: M represents a metal having an oxidation number 0 chosen fromthe group 8 metals in the Periodic Table as published in the Handbook ofChemistry and Physics, 65th Edition 1984-1985 X represents O, NR_(a) orCR_(f)R_(g); Y₁ and Y₂ represent, independently of each other,CR_(b)R_(c) or SiR_(d)R_(e); R₁, R_(w), R₅ and R₆, which are identicalor different, are chosen from a hydrogen atom, an alkyl group and anaryl group optionally substituted with alkyl; R₃, R₄, R_(a), R_(b),R_(c) are independently chosen from a hydrogen atom; an alkyl group; anacyl group; an aryl group optionally substituted with alkyl; acycloalkyl group optionally substituted with alkyl; and an arylalkylgroup in which the aryl portion is optionally substituted with alkyl;R_(d) and R_(e) are independently chosen from alkenyl; alkynyl; alkyl;alkoxy; acyl; aryl optionally substituted with alkyl; cycloalkyloptionally substituted with alkyl; and arylalkyl in which the arylportion is optionally substituted with alkyl; or alternatively when Y₁and Y₂ independently represent SiR_(d)R_(e), two R_(d) groups linked totwo separate silicon atoms together form a chain of formula:

in which n is an integer from 1 to 3; X is as defined above; R and R′,which are identical or different, take any one of the meanings givenabove for R_(e), it being understood that when N is 2 or 3, a singlesilicon atom of said chain may be substituted with one or two alkenyl oralkynyl groups; or alternatively when Y₁ and Y₂ independently representSiR_(d)R_(e), two R_(d) groups linked to separate silicon atoms togetherform a saturated hydrocarbon chain, the two R_(b) groups together withsaid silicon atoms and X forming a 6- to 10-membered ring; oralternatively when Y₁ and Y₂ independently represent CR_(b)R_(c), twoR_(b) groups linked to separate carbon atoms together form a saturatedhydrocarbon chain, the two R_(b) groups together with the carbon atomscarrying them and X form a 6- to 10-membered ring; and R_(f) and R_(g)represent, independently of each other, a hydrogen atom; an alkyl group;an acyl group; an aryl group optionally substituted with alkyl; acycloalkyl group optionally substituted with alkyl; an arylalkyl groupin which the aryl portion is optionally substituted with alkyl; ahalogen atom; an alkenyl group; an alkynyl group; or a group SiG₁G_(w)G₃where G₁, G₂ and G₃ are, independently of each other, alkyl; alkoxy;aryl optionally substituted with alkyl or alkoxy; or arylalkyl in whichthe aryl portion is optionally substituted with alkyl or alkoxy; Lrepresents a carbene of formula II.1 or II.2:

in which: A and B independently represent C or N, it being understoodthat when A represents N, then T₄ represents nothing and when Brepresents N, then T₃ represents nothing; T₃ and T₄ independentlyrepresent a hydrogen atom; an alkyl group; a cycloalkyl group optionallysubstituted with alkyl or alkoxy; an aryl group optionally substitutedwith alkyl or alkoxy; an alkenyl group; an alkynyl group; or anarylalkyl group in which the aryl portion is optionally substituted withalkyl or alkoxy; T₁ and T₂ independently represent an alkyl group; analkyl group which is perfluorinated or optionally substituted with aperfluoroalkyl group; a cycloalkyl group optionally substituted withalkyl or alkoxy; an aryl group optionally substituted with alkyl oralkoxy; an alkenyl group; an alkynyl group; or an arylalkyl group inwhich the aryl portion is optionally substituted with alkyl or alkoxy;or alternatively the substituents T₁, T₂, T₃ and T₄, may form in pairs,when they are located on two adjacent summits in the formulae II.1 andII.2, a saturated or unsaturated hydrocarbon chain, wherein M isplatinum having the oxidation number
 0. 12. The metal complex as claimedin claim 1, wherein R₃=R₄; R₁=R₆; R₂=R₅; and either Y₁=Y₂, or Y₁=CR_(b)¹R_(c) and Y₂=CR_(b) ²R_(c) where R_(b) ¹ and R_(b) ² together form asymmetric chain, or alternatively Y₁=SiR_(d) ¹R_(e) and Y₂=SiR_(d)²R_(e) where R_(d) ¹ and R_(d) ² together form a symmetric chain.
 13. Ametal complex of formula I

in which: M represents a metal having an oxidation number 0 chosen fromthe group 8 metals in the Periodic Table as published in the Handbook ofChemistry and Physics, 65th Edition, 1984-1985; X represents O, NR_(a)or CR_(f)R_(g); Y₁ and Y₂ represent, independently of each other,CR_(b)R_(c) or SiR_(d)R_(e); R₁, R_(w), R₅ and R₆, which are identicalor different, are chosen from a hydrogen atom, an alkyl group and anaryl group optionally substituted with alkyl; R₃, R₄, R_(a), R_(b),R_(c) are independently chosen from a hydrogen atom; an alkyl group; anacyl group; an aryl group optionally substituted with alkyl; acycloalkyl group optionally substituted with alkyl; and an arylalkylgroup in which the aryl portion is optionally substituted with alkyl;R_(d) and R_(e) are independently chosen from alkenyl; alkynyl; alkyl;alkoxy; acyl; aryl optionally substituted with alkyl; cycloalkyloptionally substituted with alkyl; and arylalkyl in which the arylportion is optionally substituted with alkyl; or alternatively when Y₁and Y₂ independently represent SiR_(d)R_(e), two R_(d) groups linked totwo separate silicon atoms together form a chain of formula:

in which n is an integer from 1 to 3; X is as defined above; R and R′,which are identical or different, take any one of the meanings givenabove for R_(e), it being understood that when N is 2 or 3, a singlesilicon atom of said chain may be substituted with one or two alkenyl oralkynyl groups; or alternatively when Y₁ and Y₂ independently representSiR_(d)R_(e), two R_(d) groups linked to separate silicon atoms togetherform a saturated hydrocarbon chain, the two R_(b) groups together withsaid silicon atoms and X forming a 6- to 10-membered ring; oralternatively when Y₁ and Y₂ independently represent CR_(b)R_(c), twoR_(b) groups linked to separate carbon atoms together form a saturatedhydrocarbon chain, the two R_(b) groups together with the carbon atomscarrying them and X form a 6- to 10-membered ring; and R_(f) and R_(g)represent, independently of each other, a hydrogen atom; an alkyl group;an acyl group; an aryl group optionally substituted with alkyl; acycloalkyl group optionally substituted with alkyl; an arylalkyl groupin which the aryl portion is optionally substituted with alkyl; ahalogen atom; an alkenyl group; an alkynyl group; or a group SiG₁G_(w)G₃where G₁, G₂ and G₃ are, independently of each other, alkyl; alkoxy;aryl optionally substituted with alkyl or alkoxy; or arylalkyl in whichthe aryl portion is optionally substituted with alkyl or alkoxy; Lrepresents a carbene of formula II.1 or II.2:

in which: A and B independently represent C or N, it being understoodthat when A represents N, then T₄ represents nothing and when Brepresents N, then T₃ represents nothing; T₃ and T₄ independentlyrepresent a hydrogen atom; an alkyl group; a cycloalkyl group optionallysubstituted with alkyl or alkoxy; an aryl group optionally substitutedwith alkyl or alkoxy; an alkenyl group; an alkynyl group; or anarylalkyl group in which the aryl portion is optionally substituted withalkyl or alkoxy; T₁ and T₂ independently represent an alkyl group; analkyl group which is perfluorinated or optionally substituted with aperfluoroalkyl group; a cycloalkyl group optionally substituted withalkyl or alkoxy; an aryl group optionally substituted with alkyl oralkoxy; an alkenyl group; an alkynyl group; or an arylalkyl group inwhich the aryl portion is optionally substituted with alkyl or alkoxy;or alternatively the substituents T₁, T₂, T₃ and T₄, may form in pairs,when they are located on two adjacent summits in the formulae II.1 andII.2, a saturated or unsaturated hydrocarbon chain, wherein the complexhas the formula:

in which: R₃ represents a hydrogen atom; a (C₁-C₈)alkyl group; or a(C₃-C₈)cycloalkyl group optionally substituted with (C₁-C₄) alkyl; T₁and T₂ are identical and represent (C₁-C₈) alkyl or (C₃-C₈) cycloalkyl.14. A method for the hydrosilylation of olefins or of acetylenederivatives, which is carried out in the presence of a catalystcomprising the metal complex of claim
 1. 15. The hydrosilylation methodas claimed in claim 14, comprising the reaction of an olefin with asiloxane having an Si—H unit.
 16. A catalytic composition comprising, asactive substance, one or more metal complexes as claimed in claim 1.